The present invention generally relates to an image information display apparatus and more particularly, to an image information display apparatus for use in a hardware window system which sequentially reads image information stored in a memory to provided multiwindow directly on the CRT without transferring the image information to another memory.
Generally, there are a software window system and a hardware window system are provided as a system for sequentially reading the image information from a plurality of windows stored in the memory to provide the multiwindow display on the CRT.
The software window system transfers a plurality of window image information stored in the memory to the other frame memory to compile the positioning, superpositioning or the like on the frame memory for a plurality of transferred windows. Thereafter, the image information compiled from the frame memory is sequentially read and displayed on the CRT. The hardware window system switches a pointer specifying the address of the memory during the scanning period of CRT for sequentially reading the image information of each window stored in the memory and displaying the image information directly on the CRT without transferring it to the frame memory or the like.
As all the image information for one picture face displayed on the CRT is transferred to the frame memory in advance for the case of the software window system, more time is taken to produce the window, while the degree of freedom is larger. As the address of the memory is switched by the pointer in the hardware window system to read the image information and to display it on the CRT, less time is taken to produce the window, while the degree of freedom is less.
Conventionally, an image information display apparatus for the hardware window system is as follows. In the image information display apparatus, the CRT image is split (the image may be split without limits up to the number of scanning lines) into strips corresponding to the optional scanning lines in the vertical direction as shown in FIG. 10. Furthermore, each of the respective strips is split (the maximum number of splits is 16) into "tile" having an optional bit width in the horizontal direction. Accordingly, a first window 51 is composed of a tile 52 of the (strip 2-tile 2) and a tile 53 of the (strip 3-tile 2). Namely, a plurality of tiles are combined to optionally change the shape of the window or to express a plurality of superposed windows. As shown in FIG. 11, the window-descriptor provided on the memory is composed of one or more strip-descriptors in the display order. The respective strip descriptors have a header and one or more tile-descriptors continuously linked in the order of the display. The header has a 00 number of scanning lines of the strip, the pointer for the strip-descriptor to be displayed next and the number of the tile-descriptors to be included in the strip. Also, the tile-descriptors have the width of the tile, the start-address in the memory, the number of bits per picture element, and so on.
An internal display-processor reads the contents of the descriptor-pointer-register 55 for every one frame to read the strip-descriptor linked in order from the first strip-descriptor of the window-descriptor to be shown by this pointer in order to display the image. For example, the strip-descriptor 56 is read into the horizontal fly-back line before moving to the display of the strip set in the inner register. A bit map data 58 specified by, for example, the tile-descriptor 57 in the strip-descriptor 56 is transferred and displayed onto the CRT and is displayed. After completion of the display of the strip-descriptor 56 in this manner, the following strip-descriptor 60 is read again into the horizontal fly-back line time in accordance with the pointer in the header 59 so as to repeat a similar operation.
However, an image information display apparatus of the conventional hardware window system has the CRT picture face split into a plurality of strips and tiles. The apparatus has the strip-descriptors and the tile-descriptors with image parameters of each strip and each tile being accommodated therein, so that the strip-descriptors composed of a plurality of tile-descriptor strings are sequentially read during the horizontal fly-back line time for every one frame in order to display them on the CRT. As a result, more time is required for the window display. Also, when a priority order for superposed windows, display positions or the like is changed, the image parameters are large and difficult to change.